A long pile artificial grass comprises a primary backing, piles longer than those of a usual artificial grass implanted on the primary backing, and a infill placed between the piles, and it has spread through various athletic-sports facilities as an artificial grass surface having elastic properties close to natural grass.
An elastic granulated infill of a granulated rubber (a crushed article of a waste tire or industrial rubber) or a thermoplastic elastomer (an EPDM or PE-based elastic resin) is used as a infill for a long pile artificial grass as shown, for example, in Japanese Patent Application Publication No. 2002-294620.
However, the conventional infill has had the following problems. Specifically, the conventional elastic granulated infill has a hardness as low as 40 to 65 in accordance with Japan Industrial Standard (JIS)-K6253 type A. For this reason, when 500 to 1,000 kg of the granulated infill is bagged as one lot and carried to a site at the time of construction, a phenomenon called blocking occurs in which the granulated infill adheres to each other under its own weight to form a lump.
Therefore, the granulated infill agglomerated into a lump at the time of construction has been loosened again and placed between the piles. Further, it is actually difficult to completely loosen the granulated infill agglomerated into a lump, and a infill lump agglomerated into a small lump not only disturbs uniform spraying or filling of the pile, but may affect elastic properties.
Also by the tread pressure applied by a user or equipment after laying and filling, infills may cause a blocking phenomenon in which the infills are joined together. This may compact the artificial grass surface and change the elastic properties of the artificial grass.
As another problem, it is necessary to replace the artificial grass structure with a new artificial grass after the elapse of a certain lifetime. Although the used artificial grass is removed after recovering the infills and then is disposed of as industrial waste, it is not environmentally desirable to dispose of it only as industrial waste.
Under these circumstances, there has recently been proposed an artificial grass-recycling technology in which part of the artificial grass is reused. For example, Japanese Patent Application Publication No. H09-242011 shows an embodiment in which a recovered artificial grass is smoothly recycled into a raw material by using an artificial grass made of a recyclable nylon 6. Japanese Patent Application Publication No. 2000-17605 shows an embodiment in which the artificial grass itself is recycled as a recycling raw material by fixing the pile to the primary backing using a thermoplastic resin.
However, Japanese Patent Application Publication Nos. H09-242011 and 2007-17605 are both premised on completely removing the placed granulated infill from the artificial grass. For this reason, it is not taken into consideration that the granulated infill gets wet with time or is stepped on and hardened, and it is almost impossible to completely remove the granulated infill entering the pile.
From a viewpoint of recycling, the elastic granulated infill is an impurity composed of a material different from the artificial grass. In order to solve the problem for recycling the granulated infill, there is considered a method in which the same material as that composing the infill is used for composing the artificial grass. Material recycling is possible by using this method because even if the granulated infill is left behind between the piles of the artificial grass, the granulated infill and the artificial grass can be treated as those composed of the same material.
However, even if they are produced by using the same material, there are still following problems. That is, when the recycled artificial grass is actually melted and mixed, the recycled article will be very hard and not as elastic as rubber. Therefore, even when it is formed into a granule and placed in the artificial grass, it has been impossible to create the softness close to natural grass which the long pile artificial grass originally has.
Thus, in order to solve the problems mentioned above, the present invention provides an artificial grass granulated infill excellent in productivity, workability, and recyclability, and an artificial grass structure using the same.